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United States Patent |
5,534,075
|
Miyawaki
,   et al.
|
July 9, 1996
|
Process for the production of glucose
Abstract
Disclosed is a process for producing high-purity glucose by saccharifying
liquefied starch with the aid of an enzyme, in which the saccharification
reaction of the liquefied starch is discontinued at a point where the
glucose content is less than 96% by weight, preferably within the range of
80 to 93% by weight, on a solid basis. The resulting saccharified solution
is filtered, concentrated and softened as required, and then fractionated
by subjecting it to column chromatography. Thereafter, the resulting
glucose fraction is recovered. This process makes it possible to produce
high-purity glucose efficiently in spite of a reduction in
saccharification time.
Inventors:
|
Miyawaki; Isamu (Tokyo, JP);
Kaneko; Kikuzo (Tokyo, JP)
|
Assignee:
|
Organo Corporation (JP)
|
Appl. No.:
|
308206 |
Filed:
|
September 19, 1994 |
Foreign Application Priority Data
Current U.S. Class: |
127/46.1; 127/46.2; 210/632; 210/656; 210/659; 210/660 |
Intern'l Class: |
C13J 001/06; C02F 001/00; C02F 001/28; B01D 015/08 |
Field of Search: |
127/46.1,46.2
210/632,656,659,660
|
References Cited
U.S. Patent Documents
3756919 | Sep., 1973 | Deaton | 127/40.
|
3817787 | Jun., 1974 | Von Hertzen et al. | 127/46.
|
4109075 | Aug., 1978 | Deaton | 536/1.
|
4133696 | Jan., 1979 | Barker et al. | 127/46.
|
4330625 | May., 1982 | Miller et al. | 127/46.
|
4614548 | Sep., 1986 | Cameron et al. | 127/46.
|
Primary Examiner: Caldarda; Glenn
Assistant Examiner: Hailey; Patricia L.
Attorney, Agent or Firm: Nixon & Vanderhye
Parent Case Text
This is a Rule 62 File Wrapper continuation of application Ser. No.
08/084,594, filed Jul. 1, 1993, now abandoned.
Claims
What is claimed is:
1. A process for producing glucose having a purity of 97% or more,
comprising the steps of:
(a) subjecting liquified starch to a saccharification reaction with
glucoamylase;
(b) discontinuing the saccharification reaction of the liquified starch at
a point where the glucose content is in the range of 80 to 93% by weight
on a solid basis;
(c) passing the resulting saccharified solution through a softening column
in which calcium and magnesium ions present in said solution are replaced
with sodium ions of a cation-exchange resin in the sodium form;
(d) passing the softened saccharified solution from step (c) through a
chromatography column packed with beads of a cation-exchange resin in the
sodium form and thereby eluting an ash-color fraction, an oligosaccharide
fraction, and a glucose fraction in this order; and
(e) recovering the resulting glucose fraction as glucose having a purity of
97% or more, the oligosaccharide fraction as starch syrup or an
oligosaccharide product and the ash-color fraction as an additive to
livestock feed; and optionally
(f) recycling the oligosaccharide fraction eluted in step (d) to the
saccharification reaction step (a).
2. A process for producing high-purity glucose as claimed in claim 1
wherein the saccharification reaction is carried out at a temperature of
55.degree. to 65.degree. C. for a period of 10 to 36 hours.
3. A process for producing high-purity glucose as claimed in claim 1
wherein the oligosaccharide fraction eluted in step (d) is recycled
directly to the liquified starch saccharification step (a).
4. A process for producing high-purity glucose as claimed in claim 1
wherein the oligosaccharide fraction eluted in step (d) is concentrated
and then recycled to the liquified starch saccharification step (a).
5. A process for producing high-purity glucose as claimed in claim 1
wherein the saccharified solution is filtered and concentrated before
being introduced to the chromatography column in step (d).
6. A process for producing glucose having a purity of at least 98%
comprising the successive steps of:
(a) subjecting liquified starch to an enzymatic saccharification reaction
with glucoamylase at a temperature of 55.degree. to 65.degree. C. for a
period of 10 to 36 hours;
(b) discontinuing the saccharification reaction of the liquified starch at
a point where the glucose content is in the range of 80 to 93% by weight
on a solid basis;
(c) passing the resulting saccharified solution through a softening column
in which calcium and magnesium ions present in said solution are replaced
with sodium ions of a cation-exchange resin in the sodium form;
(d) passing the softened saccharified solution from step (c) through a
chromatography column packed with beads of a cation-exchange resin and
thereby eluting an ash-color fraction, an oligosaccharide fraction, and a
glucose fraction in this order;
(e) recovering the resulting glucose fraction as glucose having a purity of
at least 98%; and optionally
(f) recycling the oligosaccharide fraction eluted in step (d) to the
saccharification reaction step (a).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for producing high-purity glucose
(grape sugar) by saccharifying starch with the aid of an enzyme and, more
particularly, to such a process for producing glucose wherein the
saccharification time of starch is reduced so as to enhance operating
efficiency and facilitate quality control.
2. Description of the Prior Art
Generally, the process for producing high-purity glucose by saccharifying
starch with the aid of an enzyme can be schematically represented by the
following flow sheet:
(Starch milk preparation step).fwdarw.(Starch milk liquefaction
step).fwdarw.(Saccharification step).fwdarw.(Filtration
step).fwdarw.(Intermediate concentration step) .fwdarw.(Activated carbon
decolorization step).fwdarw.(Deionization refining step).
In order to produce high-purity glucose in this process, it is necessary to
add a saccharifying enzyme to the liquefied starch solution resulting from
the above starch milk liquefaction step and carry out its saccharification
until a saccharified solution usually having a glucose content of 97% by
weight or greater is obtained. For this purpose, the residence time in a
batch type saccharification tank should be as long as 40 to 60 hours at a
temperature of 55.degree. to 65.degree. C. Since such a long time is
required for saccharification, large-scale saccharification equipment and
a large site are needed in order to secure certain outputs. Moreover, such
a long saccharification time also requires the implementation of strict
quality control in order to inhibit the propagation of microorganisms,
suppress the formation of impurities, and control the pH level during
saccharification. Thus, the prior art production process leaves much to be
desired with regard to the production efficiency and production control of
glucose.
SUMMARY OF THE INVENTION
In view of the above-described drawbacks to the prior art, the primary
object of the present invention is to reduce the saccharification time
(i.e., the residence time of the liquefied starch solution in the
saccharification tank) by discontinuing the saccharification reaction in
the course of the saccharification step of a glucose production process
and separating the resulting saccharified solution into a plurality of
fractions by column chromatography, so that the quality control labor
conventionally required in the saccharification step may be minimized and
the production efficiency may be enhanced without using a large-scale
saccharification tank.
In order to accomplish this object, the present invention provides a
process for producing high-purity glucose by saccharifying liquefied
starch with the aid of an enzyme, which comprises the steps of
discontinuing the saccharification reaction of the liquefied starch at a
point where the glucose content is less than 96% by weight on a solid
basis, fractionating the resulting saccharified solution by subjecting it
to column chromatography, and recovering the resulting glucose fraction.
By discontinuing the saccharification reaction at an intermediate point
and fractionating the resulting saccharified solution by column
chromatography, high-purity glucose can be obtained in spite of the
reduction in saccharification time. Thus, it is possible to enhance the
production efficiency, reduce the size of the saccharification equipment,
and save much of the quality control labor required to inhibit the
propagation of microorganisms, suppress the formation of impurities, and
control the pH level. Moreover, this production process makes it possible
to employ a columnar saccharification method using a column charged with
an immobilized saccharifying enzyme or a continuous saccharification
method using a tubular reactor or the like in place of a conventional
batch type saccharification tank.
In a preferred embodiment of the saccharification reaction in the
above-described production process, the saccharification reaction is
discontinued at a point where the glucose content is within the range of
80 to 93% by weight (hereinafter, percentages are by weight unless
otherwise stated), or the saccharification reaction is carried out at a
temperature of 55.degree. to 65.degree. C. for a period of 10 to 36 hours.
This causes the above-described effects to become more conspicuous.
In a preferred embodiment of the chromatographic fractionation in the
above-described production process, the plurality of eluate protions
obtained by column chromatography are collected into a glucose fraction,
an oligosaccharide fraction and an ash-color fraction. When the eluate is
separated into these three fractions, the oligosaccharide fraction may be
concentrated, purified and utilized as starch syrup or other
oligosaccharide products, and the ash-color fraction may be utilized as a
constituent of livestock feed after or without being concentrated. Thus,
byproducts from the glucose production can be utilized effectively.
Moreover, the yield of glucose can be enhanced by recycling the
oligosaccharide fraction to the liquefied starch saccharification step
after or without being concentrated.
Furthermore, in the above-described production process, the efficiency of
the fractionation by column chromatography can be enhanced by filtering
and concentrating the saccharified solution before subjecting it to column
chromatography, and/or by passing the saccharified solution through a
softening column before subjecting it to column chromatography.
The efficiency of the fractionation by column chromatography can further be
enhanced when the packing material used for column chromatography is an
ion-exchange resin (preferably a cation-exchange resin and more preferably
a strongly acidic cation-exchange resin) and when the packing material of
the softening column is the same as the packing material used for column
chromatography.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the relationship between the saccharification
reaction time of liquefied starch and the glucose content of the
saccharified solution; and
FIG. 2 is a graph showing the separation of glucose by chromatographic
fractionation in the example which will be given later.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein, the term "high-purity glucose" usually means glucose having
a purity of 97% or greater and preferably 98% or greater. However, the
production process of the present invention is also applicable to cases
where the desired purity of glucose is lower.
The material saccharified in the present invention is starch (such as corn
or potato starch) which has been liquefied. The liquefaction of starch can
be carried out according to any conventional procedure. Usually, starch is
reacted at a temperature of about 95.degree. to 100.degree. C. for a
period of about 1 to 2 hours in the presence of .alpha.-amylase that
liquefies starch by hydrolytically splitting linkages within the substrate
molecules.
Then, the liquefied starch is saccharified. The enzyme used for this
purpose is usually glucoamylase that acts on the nonreducing terminals of
starch to form glucose. Generally, where liquefied starch is saccharified
with the aid of an enzyme, the relationship between the saccharification
reaction time and the glucose content of the saccharified solution is as
shown in FIG. 1. Specifically, the glucose content does not exhibit a
linear increase, but a logarithmic increase in which the slope of the
curve is steep at the beginning and becomes gentler gradually. Although
the curve shown in FIG. 1 was obtained by carrying out the
saccharification reaction under the conditions employed in the example
which is will be given later, a similar relationship is observed even
under other conditions. In order to produce high-purity glucose (i.e.,
glucose having a purity of 97% or greater), it has been necessary in the
conventional saccharification process to continue the saccharification
reaction until the glucose content of the saccharified solution reaches
96% or greater (usually 97% or greater). Thus, in the case shown in FIG.
1, it has been necessary to carry out the saccharification reaction for a
period of 46 hours or more (usually 48 hours or more). The aforementioned
shortcoming or longer reaction time is of the prior art are attributable
to the fact that the saccharification rate is not constant but shows a
logarithmic change. More specifically, in order to produce high-purity
glucose, it is necessary to raise the glucose content of the saccharified
solution to 96% or greater. In the case shown in FIG. 1, the glucose
content increases to 80% in 10 hours after initiation of the
saccharification reaction. Thereafter, the glucose content increases by
10% and reaches 90% in another 14 hours (24 hours after initiation of the
saccharification reaction), and then increases by only 6% and reaches 96%
in another 22 hours (46 hours after initiation of the saccharification
reaction). Thus, it takes as long as 22 hours for the glucose content to
increase from 90% to 96%. A much longer time will be required to increase
the glucose content to greater than 96%. Such a marked lowering of the
saccharification rate with time causes considerable time and labor to be
spent.
In the present invention, high-purity glucose can be produced by carrying
out the saccharification reaction for a relatively short period of less
than 46 hours (preferably within the range of 10 to 36 hours),
discontinuing it at a point where the glucose content is less than 96%
(preferably within the range of 80 to 93%), and fractionating the
resulting saccharified solution by column chromatography to separate
glucose. Thus, after the saccharification reaction is initiated, the
saccharification is allowed to proceed efficiently for a period of time
where the saccharification rate is high, and the final stage of
saccharification in which the saccharification rate becomes lower is
omitted. This can enhance the efficiency of the saccharification step
remarkably. The most efficient period of time may be properly chosen
according to the type, activity and amount of enzyme used for
saccharification. Usually, a reaction time of 24 hours or so makes it
possible to produce high-purity glucose most efficiently. If the reaction
time is too short, the saccharification of the liquefied starch does not
proceed satisfactorily, resulting in an insufficient formation of glucose
and a low yield of glucose. However, where it is desired to produce, in
addition to glucose, other saccharides such as oligosaccharides, the
saccharification reaction may be allowed to proceed to a degree suitable
for that purpose. If the reaction time is too long, the application of the
present invention is meaningless. The saccharification reaction time can
readily be controlled by monitoring changes in the light transmittance (or
clarity) of the saccharified solution instead of measuring its glucose
content at regular intervals.
Basically, the saccharification reaction itself can be carried out
according to any conventional procedure. The liquefied starch used for the
saccharification reaction may have a total solid content of about 30 to
37% and a pH of about 4.5 to 5.0. The enzyme used for this purpose is
glucoamylase, and may be added in an amount of about 50 to 80 AGU
(Amyloglucosidase Units)/liter. The reaction temperature may be within the
range of about 55.degree. to 65.degree. C.
The resulting saccharified solution is subjected to filtration,
concentration and decolorization steps as required, and then fractionated
by column chromatography. High treating efficiency can be achieved if the
saccharified solution introduced into the chromatographic column has a
total solid content of about 58 to 62% and a pH of about 5.5 to 7.0. In
the chromatographic column, any packing material capable of selectively
separating glucose, such as ion-exchange resins, zeolite, alumina and
other porous packing materials, may be used. In the present invention, any
of various chromatographic techniques including gel permeation
chromatography, adsorption chromatography, partition chromatography,
ion-exchange chromatography and the like may be employed. Since glucose to
be separated has a molecular weight different from those of other
components such as oligosaccharides, the saccharified solution can be
fractionated on the basis of differences in molecular size. However, it is
preferable to use an ion-exchange resin (in particular, a cation-exchange
resin) as the packing material and fractionate the saccharified solution
on the basis of differences in affinity. Although cation-exchange resins
include weakly acidic cation-exchange resins (in H form) and strongly
acidic cation-exchange resins (in Na form), the resins in Na form are
preferred in that, since their affinity for glucose is greater than that
for other components (i.e., oligosaccharides and ash-color components),
glucose is eluted from the column later and high separating efficiency is
achieved. Moreover, the use of the cation-exchange resin in Na form also
has the advantage that oligosaccharides can be separated from ash-color
components and utilized effectively.
The saccharified solution may be passed through the chromatographic column
either in a batch (one pass) flow process or in a circulating flow
process. The batch flow process can be carried out by spotting the
saccharified solution intermittently and collecting the glucose fraction
while monitoring the eluate at the outlet of the column. It is convenient
that the eluate portions from the chromatographic column are collected
into an ash-color fraction, an oligosaccharide fraction and a glucose
fraction. Especially in the batch flow process, the process conditions
should be adjusted so that the difference in elution rate between the
glucose and oligosaccharide fractions is maximized. Usually, the
saccharified solution is separated into ash-color, oligosaccharide-rich,
oligosaccharide, glucose-rich and glucose fractions, and the glucose
fraction and a portion of the glucose-rich fraction are recovered as
glucose. In the circulating flow process, glucose can be selectively
recovered by recycling the oligosaccharide fraction alone, or both the
oligosaccharide and the glucose-rich fraction, to the column, or by
spotting an additional portion of the saccharified solution between the
circulating glucose and oligosaccharide fractions. The flow rate may be
suitably adjusted according to the type and volume of the packing material
used.
Thus, it is also possible to recover the oligosaccharide and ash-color
fractions concurrently separated by the chromatographic fractionation. The
former fraction may be recycled to the saccharification step or utilized
as starch syrup or an oligosaccharide product containing oligosaccharides
such as maltose, maltotriose, maltotetraose and maltopentaose. The latter
fraction may be discarded or utilized as a constituent of livestock feed.
In the production process of the present invention, the saccharified
solution is preferably softened by passing it through a softening column,
prior to the chromatographic fractionation. The main purpose of this
pretreatment is to soften the saccharified solution (i.e., to replace
calcium and magnesium ions with sodium ions and thereby reduce its
hardness). The introduction of the softened saccharified solution into the
chromatographic column is effective in maintaining the packing material in
sodium form and thereby keeping the performance of chromatographic
fractionation constant. Moreover, the passage of the saccharified solution
through a softening column prior to the chromatographic column can
effectively prevent contamination of the packing material used for the
chromatographic fractionation. Preferably, the hardness of the
saccharified solution is reduced to 0 to 0.5 mg (as CaCO3)/liter as a
result of the softening treatment. No particular limitation is placed on
the type of packing material used in the softening treatment step, and any
of various packing materials such as ion-exchange resins, zeolite, alumina
and other porous packing materials may be suitably used. However, the
efficiency of glucose separation in the chromatographic fractionation can
be significantly enhanced by using the same packing material as that used
for the softening column. Since cation-exchange resins are especially
preferred for use as the packing material of the chromatographic column,
it is preferable to use a cation-exchange resin as the packing material
for the softening pretreatment.
Steps other than those described above can basically be carried out
according to any conventional procedure.
The present invention is further illustrated by the following example.
However, this example is not to be construed to limit the scope of the
invention.
Example 1
To 1 liter of a 30% aqueous solution of cornstarch was added 0.5 g of
.alpha.-amylase (Termamyl 60L, a product of Novo, Nordisk). The resulting
solution was adjusted to pH 6.5 and then reacted at 90.degree. C. for 2
hours to liquefy the corn starch. This solution was adjusted to pH 4.5,
followed by the addition of 0.2 g of glucoamylase (AMG-300L, a product of
Novo, Nordisk; activity 250 AGU/g). The resulting solution was
saccharified at 60.degree. C. for 24 hours.
The saccharified solution was filtered through diatomaceous earth and then
concentrated to obtain a solution having the following properties:
______________________________________
Bx 60.2
pH 4.39
Electric conductivity
170 .mu.S/cm (at Bx 30)
Clarity (-log T.sub.720 nm)
0.015 (10 mm cell, pH 7)
(-log T.sub.420 nm)
0.060 (10 mm cell, pH 7)
Total cations 550 mg (as CaCO.sub.3)/liter
Total hardness 250 mg (as CaCO.sub.3)/liter
______________________________________
This solution was passed through a column packed with 100 ml of a
cation-exchange resin for softening treatment (Amberlite IR-120B in Na
form with particle sizes within a range of 0.45 to 1.0 mm accounting for
more than 90%) to obtain a solution having the following properties:
______________________________________
Bx 58.0
pH 4.8
Total cations 550 mg (as CaCO.sub.3)/liter
Total hardness 0 mg (as CaCO.sub.3)/liter
Sugar composition (measured
by HPLC)
Ash-color 6.7%
Oligosaccharides 5.3%
Glucose 88.0%
______________________________________
This solution was introduced into a column chromatographic apparatus as
described below and fractionated under the following conditions:
______________________________________
Packing material Cation-exchange resin in
Na form (the same as
that used for softening
treatment, except that
particle sizes falling
within a range of 0.22
to 0.33 mm accounting for
more than 90%),
300 ml, 1-meter bed
depth
Feed solution supplied
22.5 ml
Eluent 1/10,000 N NaOH
Eluent flow rate LV = 3
______________________________________
The results of fractionation are shown in TABLE 1 and FIG. 2 (where "L/L-R"
represents the volume of eluate per unit volume of the packing material).
A glucose solution having a glucose content of 99.6% was obtained by
recovering fraction Nos. 20-28. The recovery of glucose was 95.6%.
TABLE 1
______________________________________
Eluate Eluate Concentration (g/l)
Glucose
Sample Sampled Ash- Oligosac- content
No. L/L-R color charides
Glucose (%)
______________________________________
Feed 0.00 48.24 38.16 657.79 88.39
solution
1 0.35 0.00 0.00 0.00 0.00
2 0.37 3.98 0.00 0.00 0.00
3 0.38 3.98 0.00 0.00 0.00
4 0.40 12.33 0.00 0.00 0.00
5 0.42 36.52 0.00 0.00 0.00
6 0.44 34.37 0.00 0.00 0.00
7 0.45 34.14 0.81 0.00 0.00
8 0.47 27.51 2.16 0.00 0.00
9 0.49 22.95 3.57 0.00 0.00
10 0.50 17.93 4.96 0.00 0.00
11 0.52 12.84 6.76 0.00 0.00
12 0.54 9.68 9.56 0.00 0.00
13 0.55 7.18 12.13 0.00 0.00
14 0.57 5.34 14.49 0.00 0.00
15 0.59 4.01 16.78 0.00 0.00
16 0.60 2.98 18.67 0.00 0.00
17 0.62 1.66 20.45 0.00 0.00
18 0.64 1.33 21.73 0.00 0.00
19 0.66 0.00 19.97 58.21 74.46
20 0.67 0.00 5.15 572.84 99.11
21 0.69 0.00 2.67 763.21 99.65
22 0.71 0.00 1.51 586.12 99.74
23 0.72 0.00 0.84 333.99 99.75
24 0.74 0.00 0.33 216.95 99.85
25 0.76 0.00 0.12 139.60 99.91
26 0.77 0.00 0.04 91.44 99.95
27 0.79 0.00 0.02 51.90 99.96
28 0.81 0.00 0.01 25.00 99.96
______________________________________
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